In many applications, Hall sensors are employed to detect a position or an angle of a magnetic source placed over the Hall sensors. For example, there are increased requirements for navigations keys or pointing devices in the area of smart handheld devices and cell phones. In former solutions, four switches for different directions were used for such purposes. However, such a solution is not sufficient anymore to provide good navigation and selection means for upcoming applications. Therefore, Hall sensor signals are evaluated to determine a movement or a rotation with a certain resolution.
It is desirable to have sufficient resolution even for small movement ranges of the navigation knob. Furthermore, robustness against dust, humidity and light is desirable, wherein such robustness should be maintained during the lifetime of the respective circuit. The described features can be provided by a contactless magnetic solution employing Hall sensors.
However, smart sensors using Hall sensors need special treatment to compensate for or to correct possible imperfections of the Hall sensors used. These are mainly the offset voltage, a sensitivity drift and a low signal level. To compensate for these effects, a feedback loop can be used which reduces a major part of the offset. Further parts of the offset can be reduced by noise shaping and filtering. Such a solution can provide results with a sufficient resolution and accuracy. However, as all of the described measures have to be employed continuously, such a circuit has higher power requirements.
As in the area of smart handheld devices and cell phones power efficiency cannot be neglected, it is desirable to have Hall sensor arrangements which are able to provide sensing signals with good resolution, efficient accuracy and improved power efficiency.